fix(Core): disable StatusIcon ColorOverlay if no color is supplied

This is needed to have the underlying SVG's color bleed through and
make use of the image's opacity at the same time.

Using `ColorOverlay` together with (half) transparent colors doesn't
work very well as it makes the underlying SVG color come through,
result in wrong colors.

Applying `opacity` on the image itself cause the `ColorOverlay` to
reduce in opacity as well. So in order to work with transparent
colors, we need a way to turn of the ColorOverlay and work with the
Image's opacity, which is what this change enables.

src/StatusQ/Core/StatusIcon.qml

@@ -3,7 +3,7 @@ import QtGraphicalEffects 1.13
 
 Image {
     property string icon: ""
-    property color color
+    property string color: ""
 
     id: statusIcon
     width: 24
@@ -19,7 +19,7 @@ Image {
     }
 
     ColorOverlay {
-        visible: statusIcon.color !== undefined
+        visible: !!statusIcon.color
         anchors.fill: statusIcon
         source: statusIcon
         color: statusIcon.color